I'd just like to mention the scale on the performance graph. In Crysis, the GTX 280 is just above 1.8 which means that it performs ~1.8x the speed of the 3870x2. That would be ~36fps for the 280 then if the 3870x2 runs at 20fps.

It seems like the average performance increase is 80% compared with the 3870x2 (ie, not even double the performance), certainly nowhere near four times. This is of course assuming that nVidia haven't chosen specific resolutions and quality settings that make the GTX seem better than it really is, which wouldn't surprise me.